1. Field of the Invention
The present invention relates to a socket with a lamp without a metallic base which socket is mounted on an electrically conductive board, such as a print board or a flexible board, when used, and to a method of manufacturing such a socket.
2. Background Information
One example (the first example) of a lamp without a metallic base which has been used as a small lamp for display, indication or illumination of guages, is a lamp generally called a wedge base lamp, and a socket thereof. This example employs a socket device in which: a pair of metallic electrode contact-strips are arranged inside a socket body which is previously formed of an electrically insulating material such as a synthetic resin; and the contact-strips mechanically clamp the wedge base of the lamp to hold the lamp inserted in the body and thus to electrically connect to lead wires laid on the outside of the base.
This socket device is constructed so that it is fitted and fixed in a mounting hole portion of an exterior conductive board and that, at the same time, the board electrodes and the contact-strips pressingly contact each other to form an electrical connection.
However, in such a construction of a socket having a lamp without a metallic base, the pressed contact between the lead wires and the contact-strips is sometimes insufficient, or contact failure between the lamp and the contact-strips may be caused by, e.g., deterioration of the elasticity of the contact-strips caused by use over time, which is likely to result in lighting failure or accidental flickering. Further, because of the construction and shape of such a socket, the socket has a drawback in that it fails to meet a strong contemporary market demand, i.e. the downsizing of lighting devices.
In order to solve such problems, an alternate structure of the contact portion (the second example) has recently been proposed and put into use. In the structure, instead of the metallic contact-strips in the above socket, lamp lead wires coiled around a portion of a flange of the socket body are used to directly contact the electrodes of the conductive board.
The second example, a so-called sub-miniature lamp type, achieves a downsizing of the entire lighting device including the lamp.
Since such a structure does not require complicated bent contact-strips, it avoids lighting failure resulting from the contact-strips. However, since the contact portion is formed by coiling the lead wires, the structure (without contact-strips) has its own problems. Because the contact portion around which the lead wires are coiled lacks elasticity, changes in the socket body over time caused by the heat cycle effect of the lamp being turned on and off may result in lighting failure. Tension on the lead wires occurring during the coiling process may act on a lamp sealing portion whose strength is reduced by glass internal strain caused during processing In such a case, a crack or slow leakage may occur. Further, if the lead wires coiled around the portion contacting the electrodes of an exterior board have wrinkles, a lighting failure may occur. Also, the lead wires are required to be relatively long for the coiling process. Such long lead wires makes it difficult to automate the coiling process or to achieve high-quality products because of the difficulty in maintaining the shape of the long lead wires. Still further, since the lead wires are used as contact points, a secondary process, i.e., plating the lead wires, is required at the final stage of the lamp manufacturing, in order to prevent oxidation of the contact surfaces. Thus, costs associated with this type of structure are appreciably higher.
In order to solve the problems set forth in the second example, a contact-strip structure and means for mounting such contact-strips has a proposed. In this third example, lead wires of a lamp are integrally pre-connected to previously-prepared contact-strips of a socket by, e.g. electric welding means. Then, such contact-strips are fixed to the socket at the same time the lamp is mounted on the socket.
However, with such a contact-strip structure and means for mounting the sockets, the operations of forming lead wires and positioning the lead wires to contact-strips as pre-processes of the electric welding process are difficult. Also, since the relatively bulky metal terminals are connected to the tips of the pliable and fine lead wire by the electric welding process, such contact-strips wobble and hardly stay in position or may be tangled and trapped by each other, before the lamp and two contact-strips are mounted on a socket body. Thus, aligning and restricting the parts for automatization of the mounting process on socket bodies is extremely difficult.
Therefore, realization of the structure and mounting means of the third example is reconsidered because of the anticipated problems in production cost and quality consistency.
Still another example of lighting devices of this type (the fourth example) has been proposed, in which, simultaneously with mounting contact-strips onto a socket body, lead wires of a lamp mounted beforehand are sandwiched between the contact-strips and grooves on the body to make connections between the lead wires and the contact-strips. However, in the fourth example, it is difficult to automatize the complicated mounting operations such as proper sandwiching of lead wires.